Database Systems: Design, Implementation, and Management Tenth Edition - PowerPoint PPT Presentation

About This Presentation
Title:

Database Systems: Design, Implementation, and Management Tenth Edition

Description:

Database Systems: Design, Implementation, and Management Tenth Edition Chapter 4 Entity Relationship (ER) Modeling * Database Systems, 10th Edition * Developing an ER ... – PowerPoint PPT presentation

Number of Views:459
Avg rating:3.0/5.0
Slides: 51
Provided by: facComtec
Category:

less

Transcript and Presenter's Notes

Title: Database Systems: Design, Implementation, and Management Tenth Edition


1
Database Systems Design, Implementation, and
ManagementTenth Edition
  • Chapter 4
  • Entity Relationship (ER) Modeling

2
Objectives
  • In this chapter, students will learn
  • The main characteristics of entity relationship
    components
  • How relationships between entities are defined,
    refined, and incorporated into the database
    design process
  • How ERD components affect database design and
    implementation
  • That real-world database design often requires
    the reconciliation of conflicting goals

3
The Entity Relationship Model (ERM)
  • ER model forms the basis of an ER diagram
  • ERD represents conceptual database as viewed by
    end user
  • ERDs depict databases main components
  • Entities
  • Attributes
  • Relationships

4
Entities
  • Refers to entity set and not to single entity
    occurrence
  • Corresponds to table and not to row in relational
    environment
  • In Chen and Crows Foot models, entity is
    represented by rectangle with entitys name
  • The entity name, a noun, is written in capital
    letters

5
Attributes
  • Characteristics of entities
  • Chen notation attributes represented by ovals
    connected to entity rectangle with a line
  • Each oval contains the name of attribute it
    represents
  • Crows Foot notation attributes written in
    attribute box below entity rectangle

6
(No Transcript)
7
Attributes (contd.)
  • Required attribute must have a value
  • Optional attribute may be left empty
  • Domain set of possible values for an attribute
  • Attributes may share a domain
  • Identifiers one or more attributes that uniquely
    identify each entity instance
  • Composite identifier primary key composed of
    more than one attribute

8
(No Transcript)
9
Attributes (contd.)
  • Composite attribute can be subdivided
  • Simple attribute cannot be subdivided
  • Single-value attribute can have only a single
    value
  • Multivalued attributes can have many values

10
(No Transcript)
11
Attributes (contd.)
  • MN relationships and multivalued attributes
    should not be implemented
  • Create several new attributes for each of the
    original multivalued attributes components
  • Create new entity composed of original
    multivalued attributes components
  • Derived attribute value may be calculated from
    other attributes
  • Need not be physically stored within database

12
(No Transcript)
13
Relationships
  • Association between entities
  • Participants are entities that participate in a
    relationship
  • Relationships between entities always operate in
    both directions
  • Relationship can be classified as 1M
  • Relationship classification is difficult to
    establish if only one side of the relationship is
    known

14
Connectivity and Cardinality
  • Connectivity
  • Describes the relationship classification
  • Cardinality
  • Expresses minimum and maximum number of entity
    occurrences associated with one occurrence of
    related entity
  • Established by very concise statements known as
    business rules

15
(No Transcript)
16
Existence Dependence
  • Existence dependence
  • Entity exists in database only when it is
    associated with another related entity occurrence
  • Existence independence
  • Entity can exist apart from one or more related
    entities
  • Sometimes such an entity is referred to as a
    strong or regular entity

17
Relationship Strength
  • Weak (non-identifying) relationships
  • Exists if PK of related entity does not contain
    PK component of parent entity
  • Strong (identifying) relationships
  • Exists when PK of related entity contains PK
    component of parent entity

18
(No Transcript)
19
(No Transcript)
20
Weak Entities
  • Weak entity meets two conditions
  • Existence-dependent
  • Primary key partially or totally derived from
    parent entity in relationship
  • Database designer determines whether an entity is
    weak based on business rules

21
(No Transcript)
22
(No Transcript)
23
Relationship Participation
  • Optional participation
  • One entity occurrence does not require
    corresponding entity occurrence in particular
    relationship
  • Mandatory participation
  • One entity occurrence requires corresponding
    entity occurrence in particular relationship

24
(No Transcript)
25
(No Transcript)
26
Relationship Degree
  • Indicates number of entities or participants
    associated with a relationship
  • Unary relationship
  • Association is maintained within single entity
  • Binary relationship
  • Two entities are associated
  • Ternary relationship
  • Three entities are associated

27
(No Transcript)
28
(No Transcript)
29
Recursive Relationships
  • Relationship can exist between occurrences of the
    same entity set
  • Naturally found within unary relationship

30
(No Transcript)
31
(No Transcript)
32
Associative (Composite) Entities
  • Also known as bridge entities
  • Used to implement MN relationships
  • Composed of primary keys of each of the entities
    to be connected
  • May also contain additional attributes that play
    no role in connective process

33
(No Transcript)
34
(No Transcript)
35
Developing an ER Diagram
  • Database design is an iterative process
  • Create detailed narrative of organizations
    description of operations
  • Identify business rules based on description of
    operations
  • Identify main entities and relationships from
    business rules
  • Develop initial ERD
  • Identify attributes and primary keys that
    adequately describe entities
  • Revise and review ERD

36
(No Transcript)
37
(No Transcript)
38
(No Transcript)
39
(No Transcript)
40
(No Transcript)
41
(No Transcript)
42
(No Transcript)
43
(No Transcript)
44
(No Transcript)
45
(No Transcript)
46
(No Transcript)
47
Database Design Challenges Conflicting Goals
  • Database designers must make design compromises
  • Conflicting goals design standards, processing
    speed, information requirements
  • Important to meet logical requirements and design
    conventions
  • Design is of little value unless it delivers all
    specified query and reporting requirements
  • Some design and implementation problems do not
    yield clean solutions

48
(No Transcript)
49
Summary
  • Entity relationship (ER) model
  • Uses ERD to represent conceptual database as
    viewed by end user
  • ERMs main components
  • Entities
  • Relationships
  • Attributes
  • Includes connectivity and cardinality notations

50
Summary (contd.)
  • Connectivities and cardinalities are based on
    business rules
  • MN relationship is valid at conceptual level
  • Must be mapped to a set of 1M relationships
  • ERDs may be based on many different ERMs
  • UML class diagrams are used to represent the
    static data structures in a data model
  • Database designers are often forced to make
    design compromises
Write a Comment
User Comments (0)
About PowerShow.com